For some years it has been believed that nanostructuring in lieu of or in addition to standard surface texturing is a road to more efficient but still cost-effective photovoltaic cells. One way in which nanostructuring can lead to more efficient photovoltaic cells is by reducing reflection of light out of the cell, producing what has often been referred to as “black silicon.” Light that is reflected away from the sun-facing surface of the photovoltaic cell is lost in the sense that its energy cannot be converted to electricity by the photovoltaic cell.
A wide range of nanostructuring has been proposed. The present assignee has studied the formation of nanowires by etching as a road to nanostructuring, as discussed for example in U.S. Published Patent Application No. 2009/256134, now U.S. Pat. No. 8,143,143. Specifically, the use of metal-assisted etching of silicon has been widely regarded as promising.
The beneficial effects of nanostructuring are seen in the literature and in experience to be achievable with a wide range of specific shapes. A common denominator in some proposals is that the structures have geometric dimensions roughly of the order of the wavelength of the light which produces the electrical energy.
There is still a need for nanostructuring and cost-effective techniques to form it which lead to a net higher efficiency and other beneficial characteristics for photovoltaic cells.